Recently, earsets which integrate a speaker and a microphone in one body are proposed pretty much.
Such an earset may perform, in one body, a function of transferring sound to an ear canal and a function of collecting voices of a user. Therefore, generally, a speaker faces the ear canal for transfer of the sound, and the microphone is exposed to the outside to collect the voices of the user.
However, the microphone exposed to the outside collects external noises, as well as the voices of the user.
Therefore, an earset having a microphone (in-ear microphone) installed toward the ear canal has been proposed to solve the problem of external noise. However, the frequency of a voice transferred from the vocal cords to the eardrum through the Eustachian tube is in a low frequency band of about 0 to 2 KHz, and therefore, it is difficult to restore the original sound only from the sound of a low frequency band inputted into the in-ear microphone.
To solve the problem of losing high frequency bands, a technique of configuring a plurality of microphones and restoring an original sound by synthesizing voices of different frequency bands inputted into the microphones has been proposed. That is, an original sound is restored by configuring an in-ear microphone installed on the ear canal side, together with an out-ear microphone installed on the outside of an earflap, and synthesizing voices of different frequency bands inputted from the in-ear microphone and the out-ear microphone.
However, the characteristic of inner sound transferred from the vocal cords to the eardrum of an ear is different from user to user. Therefore, when the same high frequency sound restoration algorithm is applied, there is a problem in that a sound different from the real voice of a user may be restored.
Therefore, the restoration algorithm needs to be improved considering the characteristic of the inner sound that is different from user to user.